"a syntactic construction in which two negative words are used in the same clause to express a single negation."

"He didn't say nothing" MEANS- He said something.
"I ain't not never gunna do it" MEANS- I will do it.
"There is not nobody who will go" MEANS- Someone will go.
"I don't want nothing" MEANS- I want something.
"We don't need no education" MEANS- We need education.

If a man did not say nothing, that means he said something.
If a woman does not need NO education, it means that she needs SOME education...

Arlene:You're 20 years old and don't have a job!
Eli:Yeah well i aint not never gunna get one.
Arlene:that's a double negative, you oxymoron!
Eli:Huh? wuss tha?
Arlene:You cancelled yourself out, and made like ur GUNNA get a job...lord knows that aint the truth.
Eli:Stop being such a pansy ass know it all